Herein we report a facile anion-aided hydrothermal route for the controllable synthesis of CuO assemblies from chrysanthemum-like structures to highly dispersed microspheres in a high morphological yield ( similar to 100%). The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The formation mechanism was related to the classical anion-additive selective adsorption upon particles growth and the self-assembly process of building units assisted by cetyltrimethylammonium bromide. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3528941] All rights reserved.